Ditto to what Cricket said
FWIW my son scored 27th percentile on Processing Speed and 99.9th percentile on Math Fluency. Sometimes he's slow and sometimes he's fast, so I take all this with a grain of salt.
And I have a dysgraphic ds who has a significant dip in Processing Speed on the WISC - and who also has a significant dip in achievement scores marked "fluency" vs others - because they are timed and require handwritten responses. That's the type of analysis that reveals a learning disability (not just looking at IQ scores alone). Neuropsychologists also will typically run additional tests (beyond ability/achievement) to determine if an issue exists when this type of discrepancy occurs - as well as taking a detailed history, interview with parents, etc).
To the OP - the Processing Speed subtests don't require a child to be able to read or to know how to write, but being comfortable with holding a pencil and making marks might make a difference. FSIQ 140+ is a *really* high score - other than DYS and I think Duke (which I don't really know anything about - it's in a different part of the country than where I live) - I don't know of any programs that have admissions bars so high your ds couldn't get in with that FSIQ score. I also don't know if you can calculate it for the WPSSI, but for the WISC you can calculate a GAI which takes out WM and PSI scores, and most of the gifted programs we've encountered will accept GAI in place of FSIQ.
My suggestion is to watch your ds at school - be aware of the things that might have caused a dip in processing speed and *if* you notice other signs of things that might be a challenge (trouble with pencil grip, for instance, or trouble with timed tasks etc) - then seek out a full educational eval to determine if the dip exists and if it's meaningful.
Best wishes,
polarbear
